In the continuation of our studies on the stereochemistry of enzyme reactions, the main emphasis will continue to be on the steric course of reactions of one-carbon metabolism. Stereochemical questions to be addressed relate to methylenedioxy bridge formation in benzylisoquinoline alkaloids, tryptophan methylation at C-2 of indole, the methylenetetrahydrofolate reductase reaction, B12-containing enzymes involved in methyl transfers, methane formation in methanogenic bacteria and methane oxidation by methane oxygenase, and C-P bond cleavage in the degradation of ethylphosphonate. In addition, two projects initiated under other grants will be incorporated into this program. One of these deals with the stereochemical analysis of polyketide formation from chiral malonate and/or chiral acetate using purified enzymes (chalcone formation) or whole cells (some fungal metabolites). The other is the stereochemical analysis of the unique rearrangement reaction by which ribulose 5-phosphate is converted into the novel sugar, 1-deoxytetrulose 4-phosphate, a precursor of riboflavin.